Method of making a pressure filled lamp



Dec. 29, 1959 R. F. DORAN 2,918,763

METHOD OF MAKING A PRESSURE FILLED LAMP Filed Feb. 10. 1954 A: '4 M. Q ,0 1 29.!

29 E 28 E 26 E 3/ 5 INVENTOR ROBERT F. DORAN ii m United States Patent METHOD OF MAKING A PRESSURE FILLED LAMP Robert F. Duran, Floral Park, N.Y., assiguor, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Application February 10, 1954, Serial No. 409,306

7 Claims. (Cl. 53-7) This invention relates to photoflash lamps. More particularly, it relates to a tipless type photoflash lamp and to a method of making the same.

There has been a great deal of effort expended in recent years to design and develop a photoflash lamp which is considerably smaller in size, more economical to produce and not provided with the normal bayonet or screw type socket of the lamps of the prior art. Although the lamps of the prior art have been greatly reduced in size throughout the years their basic configuration has remained substantially the same, due primarily, to the manufacturing problems which were encountered when trying to change the basic design of the lamp.

While it has been recognized that some of these objectives could be realized by increasing the gas pressure within the lamp the problem of sealing such a lamp has not been solved heretofore.

The real pattern has been in making a good pressure seal in an oxidizing or even neutral atmosphere. The sealing techniques heretofore suggested have not been practicable for this purpose and as a result photoflash lamps which are actually offered for sale have been kept at less than atmospheric pressure.

It is an object of this invention to provide a flash lamp having a radically different structural design than the lamps of the prior art but yet amenable to processing techniques which will permit the lamps to be made on a practicable basis.

It is a further object of this invention to redesign the flash lamp structurally in such manner as to permit the obtaining of the maximum efliciency from the component parts of the lamp.

It is a still further object of this invention to provide a method of manufacturing lamps of the improved design in an economical manner.

It has been found that these objects and other advantages incidental thereto can be attained by giving the lamp a shot-gun, shell-like structure and by making a direct glass-to-metal or glass-enamel to metal seal.

In the drawings which illustrate an embodiment of features of this invention Figure 1 is an enlarged view of a front elevation of a photofiash lamp of this invention.

Figure 2 is a front elevation partly in section of a device suitable for use in manufacturing a flash lamp of the type illustrated in Figure l.

The flash lamp illustrated in Figure 1 of the drawings has a tubular glass envelope having a reduced and sized diameter, at the end which is sealed into the base portion of the flash lamp as shown in the drawings. This tubular envelope 10 is sealed to a metallic base cap 14 whose side walls extend upwardly a suflicient distance to embrace the reduced area 12 of the glass envelope 10. The base of the cap is provided with a circularly depressed segment as shown at 16 which provides adequate space for the seating of a contact button 18 which is sealed therein in an air impervious and electrically insulated manner. The method illustrated in the drawings is one in which a glass frit has been used to form a glass: to-metal seal between the button 18 and the seat as shown at 16 provided in the base structure 14. The glass forming the seal is shown at 20. The base there shown is provided with a centrally located opening at 22. This opening is sufliciently large to accommodate the passage of a wire lead 24 therethrough and is usually at least four times the diameter of the wire lead. This wire lead 24 is in good electrical contact with the contact button 18 but is insulated from the base cap 14 by means of a fused glass in much the same manner as is the button 18. ,A second wire lead 26 is maintained in good electrical con.- tact with the inside of the base 14. These two lead members 24 and 26 are provided near their terminus with a blob of ignition paste as shown at points 28. A thin filament 30 also connects the two lead wires 24 and 26 at these points. The inside of the envelope 10 is further provided with a material such as shredded foil 29 which is capable of serving as a source of actinic light when the lamp is flashed. The envelope 10 is, of course, sealed to the cap 14 by suitable means. The material shown in Figure 1 is a glass enamel as shown at 31 produced from a glass frit.

The envelope which is used in the making of the lamps may, of course, be made of any gas impervious material which is sufficiently transparent to permit the transmission of light which is produced therein. It should, of course, be of such characteristics that will enable it to be used without fear of flying fragments resulting from the burning of the materials within the lamp at the'time the light is being produced by such conflagration. For this reason when glass is used as the enclosing envelope it has been found advisable to coat the outside of the glass with a clear lacquer 32 which will at least serve to bind the fragments even though the envelope itself might crack due to the heat and pressure developed during the rapid burning of the materials producing the light. The tubular shape which is made use of in accordance with this invention makes it possible to provide a greater volume of the necessary oxygen within the lamp than would be possible if a lamp having similar outside proportions were used but were further provided with a restrictive area such as is usually customary with the flash lamps of the prior art which are necked down in the socket area. It has been found that lamps which have the design aboveshown can further be manufactured with the gas pressures within the lamp greater than those normally used in the lamps of the prior art. For the most part the lamps of the prior art usually contain a bit more than of an atmosphere in the form of oxygen. Lamps of the design shown herein can readily be made at pressures ranging up to 2 atmospheres while still maintaining the necessary safety factor. The lamp as shown in Figure 1 is substantially enlarged. A more accurate sized lamp is shown in Figure 2 of the drawings which illustrates the manner of fabricating these lamps.

The metal material for the base cap 14 can be chosen from a wide variety of materials. When a direct seal is made between the envelope 10 and the base cap 14 it is, of course, preferable to make use of a material which will lend itself to this purpose such as a recognized glassto-metal sealing alloy. Many materials are known to the prior art. The material can be so chosen as to have a co-efficient of contraction greater than the bulb or in the manufacture of the lamp a differential cooling sched-. ule can be effected so that from a temperature representing the set point of the enamel to the room temperature the material has an effective higher co-eflicient of contraction than the bulb. This will result in a radial compression type of seal of cap flange around the bulb. Examples of metals which are suitable for use for this purpose are as follows: Sylvanias #4 alloy and alloys 3 of the general chrome steel series such as 446 and 430. When glass frit is used in making the seal cold roll steel can be used.

There are, of course, a number of techniques which may be used to make lamps which structurally resemble the flash lamp shown in Figure 1 of the drawings. A preferred method of doing this is to first weld the electrode 26 to the inside of the base cap 14 and then coat the inside area particularly the inside wall section with a glass frit in those cases in which cold rolled steel is used rather than a glass-to-metal sealing alloy. The depression 16 on the outside of the base should also be so coated whereupon the button 18 to which the wire lead 24 has been centrally attached is placed within the seat and the two members placed within a furnace atmosphere wherein the temperature can be raised to the fusion point of the glass frit so as to form a glass enameled surface within the base cap (or, if preferred, over the entire surface of the cap) and a glass seal between the button 18 and the bottom of the base cap 14 with a glass seal furter present in the tip drawn portion of the cap at the point at which the wire lead 24 passes through the centrally positioned opening. This cap is then ready for the welding of a filament 30 across the leads 24 and 26 and the application of the ignition paste 28 which usually has a zirconium powder base.

After the material which is to provide the source of actinic light such as shredded foil 29 has been filled into the envelope the cap portion which has been prepared in accordance with the previously described method can be mounted on a metallic rod such as shown at 40 in Figure 2 of the drawings. The envelope containing the shredded foil can then be loosely seated within the annular side walls of the base cap 14 whereupon a hoodlike member 42 is placed over the glass tubular area. This hood-like member 42 as shown in Figure 2 of the drawings is further provided with a spring 44 extending upwardly from its top surface. This spring is made sufficiently long to enable it to engage the top of a bell jarlike member 50 which is then placed on top of the spring and pressed downwardly so as to hold the tubular member 10 firmly against the supported cap 14. When in this position the bell jar-like member 50 is seated on an 0 ring 52 and is pulled downwardly thereon onto an annular seat 54 by means of a screw threaded member 56 provided with an inwardly projecting flange 58 which e11- gages an outwardly projecting flange 60 of the bell jar. When the device has been assembled as indicated above the lamp is located in an hermetically sealed chamber whose only opening with the outside is through a series of holes 62 provided in the bottom end of the rod 40, which is tubular at this point and the tubular member 64 which passes through the member 54 but is hermetically sealed thereto. This tubular member 64 as shown in the drawings leads to a double T-shaped member 71, one leg 72 of which is connected to a vacuum pump and the other 74 to a source of oxygen gas with a third member 76 connected to a gauge and the fourth to the tube 64. While the component parts of the tube are within this hermetically sealed chamber the valves can be so regulated as to cause all the air to be withdrawn from within the tube through the channels formed by the normal irregularities in contact between base cap and bulb, or through the glass frit after which upon proper manipulation of the valves oxygen gas can be introduced into the chamber to any desired pressure. The pressure which has been found to be particularly suitable to date is one in the neighborhood of 1.6 atmospheres. When this oxygen pressure has been reached the radio frequency coil 70 which is shown surrounding the bell jar-like member 50 at a point close to the base cap 40 is activated. When this is done the glass enamel within the annular area of the base cap is caused to soften, wetting the bulb, after which the entire device is permitted to cool. If this is done under the proper time temperature conditions a good glass-enamel-metal seal is formed at this point and the flash lamp can be withdrawn from within the bell jar 50 and is now ready for use.

In practicing this sealing technique with the aid of a radio frequency energy applied to the side walls of the base cap it is, however, extremely necessary to provide some means for holding the heat to a desired area of the cap. Otherwise, there would be a tendency for the glass seal which has been formed between the button 18 and the base 14 to crack or at the very least become gas pervious. Furthermore, means must be provided to hold the heat as close to the bottom of the cap as possible and away from the glass tube to which it is being sealed particularly above the edge of the base for two purposes, the first being the appearance of the glass tubular member if the heat were to be allowed to cause the envelope to be deformed and secondly shielding means must be provided to keep the heat away from the ignition paste for fear of producing a pre-ignition and therefore a worthless lamp. The rod 40 as shown in Figure 2 of the drawings has been provided to act as a means for Withdrawing heat from the base cap at a sufficiently rapid rate to prevent the melting of the enamel immediately adjacent the button. To accomplish this a good heat conducting material has been chosen with a sufliciently massive structure to permit adequate heat conduction from this critical area. The member 42 besides serving to hold the tube firmly pressed against the cap member also serves as a heat shield. This member is preferably caused to extend downwardly to a point which is slightly below the top level of the base cap. This helps to isolate the direct radio frequency energy which is absorbed by the base cap 14 and hold it in the position where it will do the most good in melting the glass enamel and causing a direct glass-to-metal seal at the desired points. In a way it also serves as a heat shield and instrument for dissipating heat from undesired areas.

The projecting edge of the cap 14 not only adds strength to the structure and thereby permits the use of relatively thin metal stock but also serves as a means to help localize the heat during the sealing operation. Since the edge projects a slight distance further out from the center than does any other part of the lamp it is closest to the coil and therefore serves as the locus for the radio frequency energy as it is given off.

Projection lamps which use a neutral atmosphere can also be made in accordance with the fundamental principles of the method herein described. The characteristics of such lamps are also improved by such increase in pressure since one thereby aids in dissipating the heat given off during operation and also tends to decrease the vapor pressure of the tungsten filament. Both of these, of course, beneficially affect the life characteristics of the lamp.

While the above description and drawings submitted herewith disclose a preferred and practical embodiment of the photoflash lamp of this invention it will be understood that the specific details of construction and arrangement of parts as shown and described are by way of illustration and are not to be construed as limiting the scope of the invention.

What is claimed is:

1. In the method of making a pressure filled photoflash lamp the steps comprising placing a metallic cap to which an igniter has been attached over the open end of an envelope containing material for producing actinic light, introducing the assembled components into a charm ber whose atmosphere can be controlled, covering the envelope portion of the assembly with a metallic hood, evacuating said chamber, introducing oxygen into said chamber to the desired pressure, heating the metallic cap by RF energy to a temperature at which the cap will be wet by the materials immediately adjacent thereto thereby causing a gas impervious seal to be produced, allow ing the parts to cool and removing them from said chamber.

2. In the method of making a pressure filled photofiash lamp the steps comprising placing a metallic cap to which an igniter has been attached over the open end of an envelope containing material for producing actinic light, introducing the assembled components into a chamber whose atmosphere can be controlled, covering the envelope portion of the assembly with a metallic hood, holding the assembled components in pressure relationship with one another, evacuating said chamber, introducing oxygen into said chamber to the desired pressure, heating the metallic cap by RF energy to a temperature at which the cap will be wet by the materials immediately adjacent thereto thereby causing a gas impervious seal to be produced, allowing the parts to cool and removing them from said chamber.

3. In the method of making a pressure filled photofiash lamp the steps comprising placing a metallic cap to which an igniter has been attached over the open end of an envelope containing material for producing actinic light, introducing the assembled components into a chamber whose atmosphere can be controlled, covering the envelope portion of the assembly with a metallic hood, holding the assembled components in pressure relationship between said hood and a heat conductive rod abutting the center section of said cap, evacuating said chamber, introducing oxygen into said chamber to the desired pressure, heating the metallic cap by RF energy to a temperature at which the cap will be wet by the materials immediately adjacent thereto thereby causing a gas impervious seal to be produced, allowing the parts to cool and removinglthem from said chamber.

4. In the method of making a pressure filled photoflash lamp the steps comprising placing a glass enameled metallic cap to which an igniter has been attached over the open end of a glass envelope containing material for producing actinic light, introducing the assembled components into a chamber whose atmosphere can be controlled, covering the envelope portion of the assembly with a metallic hood, holding the assembled components in pressure relationship between said hood and a heat conductive rod abutting the center section of said cap, evacuating said chamber, introducing oxygen into said chamber to the desired pressure, heating the metallic cap to a temperature at which the glass enamel on the cap will wet the glass envelope immediately adjacent thereto thereby causing a gas impervious seal to be produced, allowing the parts to cool and removing them from said chamber.

5. In the method of making a pressure filled photoflash lamp the steps comprising placing a metallic cap to which an igniter has been attached over the open end of a glass envelope containing material for producing actinic light, introducing the assembled components into a chamber whose atm p ere. c n e controlle v rseal to be produced, allowing the parts to cool and' removing them from said chamber.

6. Apparatus for making a pressure-filled lamp said apparatus comprising: a container open at one end and having an outwardly-extending flange at said open end; a'ring of resilient material fitting under said open end; anexternally-threaded base member; means for holding said container to said base member tightly through said ring of resilient material said means comprising an internally-threaded member having an inwardly-extending flange in position to engage the outwardly-extending flange of said container and to hold it against said resilient ring, said member being threaded onto said base member; a hollow support for the parts of a lamp, said support extending through said base member and having an opening in communication with the atmosphere inside said container; evacuating and gas-filling means in communication with the interior of said hollow support; and means for heating said lamp parts to fuse them together.

7. Apparatus for making a pressure-filled lamp said apparatus comprising: a container open at one end; a ring of resilient material fitting over said open end; a base member; means for holding said container to said base member tightly through said ring of resilient material; a hollow support for the parts of a lamp, said parts including a metal piece, a glass piece and a filling of ignitable material, and said support extending through said base member and having an opening in communication with the atmosphere inside said container; evacuating and gas-filling means in communication with the interior of said hollow support; means outside said container for heating said lamp parts to fuse them together,

said means being an RF coil in position to act on the metal piece of the lamp parts; and a metal shield around said ignitable material to prevent its ignition by the RF coil.

References Cited in the file of this patent UNITED STATES PATENTS 1,679,386 Tenney Aug. 7, 1928 1,893,380 Uschmann et a1. Jan. 3, 1933 2,013,415 Marden et al. Sept. 3, 1935 2,125,316 Ronci Aug. 2, 1938 2,262,176 Geiger et al. Nov. 11, 1941 2,274,400 De Margitta Feb. 24, 1942 2,613,863 Louthan et al. Oct. 14, 1952 2,710,713 Slater June 14, 1953 

